The technical sphere of the invention concerns interpolating images, whether this insertion is temporal or stereoscopic.
Generally speaking, temporal inter-image interpolation consists of the construction and insertion of additional images by a receiving system. The restored quality of the images depends partly on the quality of the compression or restoring system.
Within the context of system for coding images with digital flow reduction (as for example the one defined by recommendation H.261 of the ITTCC (organization whose new name is UIT.T) for the coding of video at p times 64 kbit/s), a sub-sampling of the images at the coder is one of the means used. The non-transmitted images are then duplicated or interpolated by a decoder which is a simple device to significantly reduce the flow of information required for transmission of the video signal.
Various image interpolation methods using an estimation and movement compensation have been proposed (see refs 1!, 2! and 3! given at the end of the description).
An interpolated image may also be used as a prediction image in certain coding methods (this being the case for the standard of the ISO/IEC 11172.2 known as MPEG1):they are then called &lt;&lt;B-frames )), &lt;&lt;P-frames &gt;&gt;).
The temporal interpolation of images is also useful in medical applications in which it may be desired to have a patient exposed as little as possible to the image-taking device (X-rays, for example) by reducing the number of views, that is images.
Another application is the interpolation of images in cases of stereoscopy. This then concerns interpolated stereoscopic images.
The image interpolation methods are reduced in a large number of practical implementations to a single recopy from the preceding image (rereading of a memory) or to a linear insertion.
Studies based on movement estimation have been proposed by several authors (see refs 1! and 3!. Often, the calculation of the movement vectors is effected on blocks of rectangular (or square) sizes N.times.M.
The triangulation of images has in particular been proposed so as to improve image prediction in the case of inter-image diagrams with estimation/movement compensation (see refs 4! and 5!).
The notion of bi-directional image is not traditionally used with a triangle-based movement estimation, but only with a base of blocks.
In a conventional temporal interpolation method, the sequences obtained by a single recopy of the preceding image do have the drawback of being intermittent. The use of a single linear interpolation moreover produces a shadow or out-of-focus effect which prove to be totally undesirable.
In more elaborate methods, it is essential to identify several zones, such as the bottom or moving objects or to calculate segmentation masks. But the interpolations using the movement vectors obtained on blocks with a size M.times.N do not make it possible to form a continuous interpolated image derived from a dense vector field.
Known methods, which seek to obtain fields with denser and more continuous vectors, require the calculation of the vectors towards the front (future of the image (n-k) towards the image (n)) and towards the rear (moved from the image (n) towards the image (n-k)) so as to identify occlusion zones (see ref 1!). Existing methods do not make it possible to easily in a single passage obtain a field of vectors for the image to be interpolated which covers the image continuously.
One of the most important problems to resolve for interpolation via movement compensation is the determination of a movement vector for each point of the image to be inserted. Phenomena, such as occlusions, zoom effects, ambiguities concerning the nature of the point (bottom or moving object) produce gaps in the plane of the interpolated image and which need to be filled up, and ambiguities which need to be resolved so as to avoid artifacts in the interpolated image.
A document with the ref 7! at the end of the description describes an image interpolation method in which all the image elements are restored at a moment of their trajectory by using a mesh cutting the image into blocks having the shape of non-overlapping trapeziums. The movement of nodes of this mesh determines the desired deformations of the image blocks. The movements of these nodes are estimated. It is possible to carry out a refined logging by dividing each trapezium into two triangles.
So as to resolve existing problems in the devices of the prior art, the invention concerns a method able to produce interpolated images by using fields with dense continuous vectors. The invention also is concerned with minimizing the amount of information to be transmitted.